Question

The work done in blowing a soap bubble of surface tension \(0.06 \text{ N m}^{-1}\) from radius \(2 \text{ cm}\) to \(5 \text{ cm}\) is:

• A. \(0.004168 \text{ J}\)
• B. \(0.003168 \text{ J}\)
• C. \(0.003158 \text{ J}\)
• D. \(0.004568 \text{ J}\)

Hint:

Soap bubbles have two surfaces, so multiply surface energy by 2.

Answer 1

The Correct Option is B

Step 1: Work done in forming a soap bubble: \[ W = 2T \Delta A \]
Step 2: \[ \Delta A = 4\pi (r_2^2 - r_1^2) = 4\pi(25 - 4)\times 10^{-4} \]
Step 3: \[ W = 2 \times 0.06 \times 4\pi \times 21 \times 10^{-4} = 0.003168 \text{ J} \]